CN111203801A

CN111203801A - Active damping centerless grinding method

Info

Publication number: CN111203801A
Application number: CN201911118010.4A
Authority: CN
Inventors: A·阿斯塔洛亚巴迪奥拉; I·伊泽纳罗莱特
Original assignee: Ideko S Coop
Current assignee: Ideko S Coop
Priority date: 2018-11-19
Filing date: 2019-11-15
Publication date: 2020-05-29
Anticipated expiration: 2039-11-15
Also published as: ES2950908T3; CN111203801B; US20200156207A1; EP3653336B1; EP3653336A1

Abstract

The invention relates to an active damping centerless grinding method for a centerless grinding machine, the centerless grinding machine having a wheel (1, 2) and a head (5, 6) carrying the wheel (1), between the wheels A part (3) to be ground is arranged therebetween, the method comprising: moving the wheels (1, 2) close to each other in order to apply pressure on the part (3) to grind it, so that the grinding is carried out in the grinding machine due to the grinding Vibration is generated in the grinding machine; measurement of vibration due to grinding; and, according to said measurement, parallel to the force flow of the grinding machine and by using an inertial actuator (10) acting directly on one of the heads (5, 6). ) introduces an active damping force (F _act ) so that vibrations due to grinding are attenuated.

Description

Active damping centerless grinding method

Technical Field

The present invention relates to a method of grinding a component in a centerless grinding machine. The proposed method uses a control strategy that allows the introduction of active damping forces by means of inertial actuators, which attenuate the vibrations due to the grinding process itself, thus improving the accuracy of the centerless grinder.

Background

Grinding is a widely used process for performing abrasive machining operations with higher dimensional accuracy and lower roughness than stock-removal machining operations. For this reason mainly grinding is considered as a finishing method, wherein the forces of the grinding process are not too great.

In this sense, the ordinary grinding essentially focuses on improving the precision, for which reason the techniques used today focus on eliminating the constant vibrations of the machine. For example, in order to improve the accuracy of the grinding machine, documents JP2005199410A or JP2002254303A are known, which propose techniques for eliminating vibrations due to unbalance in the wheel.

However, in centerless grinding (which is a variation of conventional grinding), these constant vibrations of the machine are of less importance, since centerless grinding is used for surface machining operations, and not only for finishing operations. For this reason, in centerless grinding, it is particularly important that vibrations occur due to the grinding process itself, as in the case of self-excited vibrations (chatter).

In centerless grinding, the part is placed in the machine without any fixturing while being machined. This process is widely used to produce precision cylindrical parts with high productivity. This is mainly achieved by eliminating the operations for centering and anchoring the part to be ground, which will greatly reduce the operating time and enable automation of the grinding process. The fact that no anchoring is required means that centerless grinding also constitutes a very interesting method for machining small-sized cylindrical components starting from their surface machining operation.

Furthermore, in centerless grinding, the width of the wheel used tends to be significantly larger compared to typical grinding processes, resulting in a significant increase in the force of the grinding process. All this means that, as mentioned above, the accuracy of a centerless grinding apparatus depends primarily on vibrations (particularly chatter) generated by the grinding process itself, while typical vibrations of the machine may be of secondary importance as in the case of vibrations due to imbalance in the wheel. The vibrations of these processes are mainly dependent on the dynamic stiffness of the machine and the grinding conditions.

One of the most effective solutions for eliminating vibrations due to the process is to increase the damping by acting directly on the dynamic behavior of the grinding machine without having to know specific data of the process conditions. One way to introduce damping in a passive manner is by using a passive actuator with a suspended mass that can oscillate freely in accordance with the vibrations of the machine. If the resonance of the suspended mass coincides with the resonance of the machine, the machine may dampen the vibrations. This has the disadvantage that the suspended mass must have a quantifiable value relative to the modal mass of vibration, thus requiring a bulky actuator that can occupy a large amount of space in the machine. Furthermore, the passive actuator can only operate in a specific vibration mode and does not adapt to other different vibration modes that may occur, which makes it an unsuitable solution for damping process vibrations in centerless grinding machines, since the vibration frequency in this type of machine may vary depending on the cutting conditions.

An active damping system may be a solution for adapting to different vibration modes and damping vibrations originating from the grinding process and without requiring a very large space for arranging it. These systems generally consist of a vibration detection device, a controller that calculates the force to be applied, and an actuator that is responsible for introducing the damping force required to dampen the vibrations.

See for example document ES2278496a1, which shows an active control system for controlling self-excited vibrations in a centerless grinding machine. The system uses a piezoelectric actuator acting directly on the translation means (nut-spindle assembly) of the head of the regulating wheel of the grinding machine, while the vibrations are detected by a mechanical stress sensor also arranged in the translation means.

In this document, the piezoelectric actuator is arranged in series with the force flow of the grinding machine, i.e. the actuator is arranged in a translation device responsible for pressing the component against the head of the regulating wheel of the grinding wheel. Introducing a damping force in series with the force flow of the machine means that the actuator is focused on changing the actual stiffness of the machine, for which reason the best point to place is the point where the deformation energy generated by the vibrations is highest. With this arrangement, however, the actuator must always provide rigidity, so in the event of failure of the actuator, the machine will no longer be able to function in an appropriate manner.

On the other hand, as shown in the two documents JP2005199410A and JP2002254303A indicated above, elimination is the most widely used control strategy for solving constant vibrations of the machine (such as unbalance in the wheel).

This strategy is based on the introduction of a force that generates vibrations having the same amplitude, frequency and opposite phase with respect to the typical vibrations of the machine. In this way, complete elimination of vibrations is sought, but this requires actuators with high force capacity and accurate knowledge of the vibrations to be eliminated. For this, a detailed model of both the dynamics of the machine and the method to be damped is required. If cancellation is observed in a simple second order equation (Eq. 1), the force applied by the actuator (F)_act) It must be exactly opposite to the force (F) to be eliminated, proving that the force capacity of the actuator must be high.

However, when the vibrations originate from the grinding process, it is not possible to obtain accurate knowledge of the vibrations, and therefore cancellation cannot be used to dampen this type of vibrations. Furthermore, the use of such a control strategy to eliminate constant vibrations in the machine (e.g. unbalance in the wheel) may even lead to situations where the vibrations due to the cutting process are amplified, as elimination may cause excitation of these other vibration modes (see JP 2002254303A).

In light of the foregoing, there is a need for a process or method for a centerless grinding machine that improves the attenuation of vibrations due to the grinding process itself through the use of an active damping system.

Disclosure of Invention

The object of the invention relates to a centerless grinding method in which the vibrations generated during the grinding process are measured and an active damping force for damping the vibrations during the process is introduced by means of an inertial actuator.

The method is applied in a centerless grinding machine having wheels between which a component to be ground is arranged, and a head carrying the wheels.

The grinding method comprises the following steps:

moving the wheels closer to each other, exerting pressure on the part to grind it, so that vibrations are generated in the grinding machine as a result of the grinding,

measuring vibrations due to grinding, an

According to the results of said measurements, active damping forces are introduced parallel to the force flow of the grinding machine and by using an inertial actuator acting directly on one of said heads, so as to damp the vibrations due to grinding.

Unlike documents ES2278496a1 or JP2005199410A, in which the actuators are arranged in series with respect to the force flow of the grinding machine, the present invention proposes to introduce a damping force in parallel with the force flow of the grinding machine. In this way, when the damping force is introduced in parallel, the original characteristics of the machine are not changed, and the damping force is introduced as an external force. This ensures proper machine operation even when the actuator is not operating. When the damping forces are introduced in parallel, the optimum placement point is the point with the largest vibrational motion.

So that during grinding and detection of the occurrence of vibrations by means of the inertial actuator, it is possible to accelerate the moving mass of the actuator arranged in the head, thereby introducing the force necessary to damp said vibrations. The vibrations generated in the grinding machine during the grinding of the component are thereby attenuated or eliminated in real time and in an efficient manner.

When performing surface machining operations at high grinding forces, as in the case of centerless grinding machines, there are mainly two key vibration modes corresponding to the head open mode, i.e. the relative movement for moving the head and the component carrying the wheel closer/further away from each other occurs in the direction in which the wheel applies pressure to the component. For this purpose, it is preferred to introduce an active damping force into the upper part of at least one of the heads, since it has been experimentally identified as the point of maximum movement due to vibration.

Preferably, the vibrations are measured in both heads, while an active damping force is introduced into each head by means of a respective inertial actuator, so that the vibrations due to grinding are damped in both heads.

Preferably, the active damping force is introduced at the same point of the machine where the vibration position is measured.

Even more preferably, the vibration is measured in an upper part of the head, and an active damping force is applied in this upper part of the head.

Therefore, the detection means and the inertial actuator are used, arranged in a co-located manner (in a co-located manner), so as to make the damping of the vibrations generated in the machine more effective. Such a co-location profile is recommended in which the detection means and the inertial actuator are positioned at one and the same point, since in theory all vibration modes present in the bandwidth of the inertial actuator can be attenuated. In the case of a non-co-located distribution, as in the case of document JP2005199410A, when there are vibration modes having different phases between the measurement point and the actuation point within the bandwidth of the actuator, vibration control may be hindered.

The inertial actuator is configured for generating a movement of its moving mass as a function of the vibrations measured by the detection means. Preferably, the inertial actuators used are hydraulic actuators, electromagnetic actuators or linear motors responsible for accelerating the moving mass, allowing the introduction of controlled forces.

The choice of actuator depends on the force and frequency bandwidth required for the actuator. In centerless grinding operations, structural modes with low frequencies of less than 300Hz, in particular between 10-300Hz, are very critical, requiring a certain movement of the mass of the inertial actuator. In documents ES2278496a1 and JP2005199410A, piezoelectric actuators are used which are arranged in series with the force flow of the grinding machine. Piezoelectric actuators constitute the most widely used actuators arranged in series with the force flow of the machine, where they must have high-energy deformation energy. However, it has been observed that due to their high vulnerability, piezoelectric actuators are not suitable for forming low frequency inertial actuators that require a considerable degree of motion (as in the case of centerless grinding).

Inertia, which is the movement of the mass of the inertial actuator, introduces active damping forces in the machine, the magnitude, frequency and phase of which depend on the control strategy used.

Preferably, the control strategy used by the invention is based on measuring the speed of the vibrations due to grinding, preferably in the head, and exerting a force by means of an inertial actuator, which force is proportional to the amplitude (amplitude) of said speed, has the same frequency, but has the opposite phase. By introducing a damping force in this way, damping can be introduced which is proportional to the magnitude of the force introduced, so that the dynamic stiffness of the machine can be increased.

The control strategy can be mathematically interpreted in a simple manner based on simple equations of motion (equations 1-3), where x is the vibratory motion of the machine and m, c, and k are the mass, damping, and modal stiffness of the machine, respectively. F is the force to which the machine is subjected to be attenuated or eliminated during grinding, and F_actIs the force exerted by the inertial actuator.

This is a feedback strategy and therefore does not require knowledge of the dynamic parameters of the machine or the cutting conditions used. Furthermore, contrary to what happens with elimination strategies (as described in documents JP2005199410A and JP2002254303A), the force capacity (force capacity) required for the inertial actuator is not so large, since it is not necessary to apply a force equal to the vibration force to be attenuated.

Alternatively, a simple model of the dynamics of the machine can be developed so that the control strategy is based on making the inertial actuator behave like a passive damper (tuned mass damper). The main disadvantage of passive dampers is that they are limited to reducing a single vibration frequency and the required mass is very high. However, by an active control strategy that simulates this behavior, different frequencies can be attenuated, and it can be designed to simulate different mass magnitudes. Thus, as with the strategy set forth above, knowledge of the cutting conditions or the vibrations to be generated is not required.

Mathematically, this strategy suggests the introduction of an active damping force (F)_act) Which is the frequency (ω)_a) And the required relative damping in the virtual passive mass (ξ)_a) Where μ is the ratio between the virtual passive mass and the mass of the machine (μm ═ m)_aAnd/m). Accordingly, with this alternative control strategy, an active damping force (F) is introduced according to the following equation_act)：

Wherein:

m is the mass of the grinding machine

μ is the ratio between the virtual passive mass of the actuator and the machine mass (μm ═ m)_a/m)

x is the movement measured due to vibration

ω_aIs the desired oscillation frequency in the virtual passive mass

ξ_aIs the required relative damping in the virtual passive mass

In accordance with the foregoing, a method for grinding a component in a centerless grinding machine is obtained that improves grinding accuracy by attenuating vibrations that are generated in the machine by the grinding process itself.

Drawings

Fig. 1 shows an example of a centerless grinding machine in which the grinding method of the present invention can be applied.

Fig. 2 shows a schematic view of two main vibration modes of the machine of fig. 1.

Fig. 3 shows a schematic view of an actuator arranged in series with the force flow of the grinding machine.

Fig. 4 shows a view as in the previous figure, but with the inertial actuator as proposed by the invention arranged parallel to the force flow of the grinding machine.

Fig. 5 shows a comparison of damping forces used in an elimination control strategy according to the state of the art.

Fig. 6 shows a comparison of damping forces used in an active damping control strategy as proposed by the present invention.

Detailed Description

Fig. 1 shows an example of a centerless grinding machine in which the grinding method of the present invention can be applied. The grinding machine comprises two wheels (1, 2): a grinding wheel (1) and an adjusting wheel (2), between which a component (3) to be ground is arranged, which is supported on a holding device (4). Each wheel (1, 2) is arranged in a head (5, 6) and each head (5, 6) is arranged on a translation device (8, 9).

The machine configuration shown in fig. 1 is not limiting to the invention, and it will be apparent to those skilled in the art that the grinding method can be applied to centerless grinders having different machine configurations.

By the movement of the heads (5, 6), the wheels (1, 2) are moved closer to/away from each other in a direction perpendicular to the component (3). Thus, in operation, the wheels (1, 2) exert a pressure on the component (3) in the direction in which the wheels (1, 2) approach each other, so that the component (3) is held between the wheels (1, 2), supported so that it rotates freely about the holding device (4), whereupon the component (3) is ground by the rotation of the wheels (1, 2).

The grinding process itself generates forces that excite vibration modes of different parts of the machine, such as the heads (5, 6), which itself generates vibrations that are transmitted to the machining points in the contact area between the part (3) and the wheels (1, 2). This leads to geometrical defects or excessive wear of the working tool, or poor surface finish of the component (3), among other factors. As can be seen from fig. 2, the centerless grinder has two main vibration modes which cause the heads (5, 6) to bend causing them to move away from or closer to each other.

The invention relates to a grinding method for a centerless grinding machine, whereby vibrations caused by the grinding process itself can be reduced or even eliminated.

Therefore, the grinding method provided by the invention comprises the following steps: the wheels (1, 2) are moved closer to each other, exerting pressure on the part (3) to be groundMeasuring the vibrations due to grinding and introducing an active damping force (F) according to said measurement_act) Parallel to the force flow of the grinding machine and introduced by using an inertial actuator (10) acting on one of the heads (5, 6), so that vibrations due to grinding are damped.

For example, the vibrations due to grinding are measured using a detection device (9), such as an accelerometer. The detection means (9) are particularly configured for measuring low frequencies of less than 300Hz, and preferably measuring a frequency range between 10-300 Hz. For this purpose, it has been envisaged to use filters which discriminate between noise due to frequencies outside the preferred range described above.

As shown in the example of fig. 1, it has been envisaged that the inertial actuator is arranged on the upper part of the head (5, 6), which is part of the position of the machine where the maximum movement occurs due to the vibrations of the grinding process.

In order to improve the machine accuracy, an inertial actuator (10) is arranged in each head, so that an active damping force (F)_act) Is introduced into each head (5, 6).

The detection means (9) are arranged in the head (5, 6) such that the detection means (9) and the inertial actuator (10) introducing the force are co-located at the same point.

In the example of fig. 1, the vibrations are measured in two heads (5, 6), while an active damping force (F) is introduced in each head (5, 6) by a respective inertial actuator (10)_act) So that vibrations in the two heads (5, 6) due to grinding are damped.

Fig. 3 shows a schematic view of an actuator (9) arranged in series with the force flow of the grinding machine as proposed in documents ES2278496a1 or JP2005199410A of the state of the art, while fig. 4 shows another schematic view of an inertial actuator (9) arranged parallel to the force flow of the grinding machine as proposed by the present invention.

The force flow of the grinding machine, also referred to as the "path force", is represented in the figure by the line with arrows. This flow refers to the transfer path of the force required for grinding the part that is followed inside the machine.

As proposed by documents ES2278496a1 or JP2005199410A, when the actuators are arranged in series, the actuators can change the original dynamic characteristics of the machine because the force flow passes through them, damping the vibrations generated, while at the same time having to withstand the grinding forces. For this reason, the actuators arranged in series must provide a very high stiffness and, if the actuators fail, the machine will not be able to grind correctly.

In contrast, if the inertial actuators are arranged in parallel, as proposed by the present invention, the damping force is introduced as if it were an external force, and it has no effect on the original stiffness of the machine. For this reason, even in the event of actuator failure, the machine will still have its original stiffness and grind correctly.

According to one embodiment of the invention, active damping is performed using a control strategy based on measuring the vibration velocity of the head (5, 6) and applying a force proportional to the amplitude of this velocity by means of an inertial actuator (10).

In this sense, the force required by the actuator is not as great as it would be eliminated, and knowledge of the dynamics of the machine or the method to be damped is not required.

Active damping is used by means of feedback, as proposed by the present invention, with the aim of providing a machine with higher dynamic stiffness depending on the measured vibrations, which is highly effective for eliminating process vibrations. This feedback strategy is not effective for forcing constant vibrations, such as is the case with vibrations due to imbalance in the wheel, but it does be very effective against process vibrations, since these vibrations are completely damped by the increase in the dynamic stiffness of the machine using forces smaller than the vibration forces.

According to another embodiment of the invention, for active damping, a control strategy based on a dynamic model of the machine is used to make the inertial actuator behave like a passive damper (tuned mass damper). Such a virtual passive damper can attenuate different frequencies and can be designed to simulate different mass levels, thereby eliminating the disadvantages of passive dampers. Furthermore, the force required for the actuator will also be much smaller than in cancellation, since it is also based on feedback of the vibration parameters. Although the need for a dynamic model makes it less attractive than simple feedback, the fact that the dynamic behavior does not vary depending on the position of its components means that the model does not need to be adjusted in every process, since the control strategy does not need to know the conditions of the grinding process.

Below is shown a table comparing the control strategy based on cancellation in the case of documents JP2005199410A or JP2002254303A and the control strategy based on active damping in the case of two strategies as proposed by the present invention.

It can be seen that in other advantageous aspects, in the case of active damping, the force required by the inertial actuator is much less than that required for cancellation, and furthermore cancellation is a pre-control strategy requiring precise knowledge of the vibration to be cancelled, while active damping is a feedback strategy that does not require precise knowledge of the vibration to be damped.

FIG. 5 shows a comparative diagram for an abatement control strategy according to the state of the art, wherein the damping force (F) is depicted by a line_act) Having the same magnitude and opposite phase with respect to the force (F) to be eliminated, while fig. 6 shows a comparative graph for an active damping control strategy, in which the required damping force (F) is clearly seen_act) Less than damping force (F) for elimination_act)。

Claims

1. An active damping centerless grinding method for a centerless grinding machine having wheels (1, 2) and heads (5, 6) carrying the wheels (1, 2) , a component (3) to be ground is arranged between the wheels (1, 2), and the grinding method comprises:

moving the wheels (1, 2) close to each other, applying pressure on the part (3) for grinding it, whereby vibrations are generated in the grinding machine due to grinding,

Measure vibration due to grinding, and

According to the measurements, an active damping force (F _act ) is introduced parallel to the force flow of the grinder and by using an inertial actuator ( 10 ) acting directly on one of the heads ( 5 , 6 ) , so that the vibration caused by grinding is attenuated.

2. Active damping centerless grinding method according to the preceding claim, characterized in that the active damping force (F _act ) is introduced into the upper part of the head (5, 6).

3. Active damping centerless grinding method according to any of the preceding claims, characterized in that vibrations are measured in the head (5, 6), while the active damping force (F _act ) is passed through the corresponding An inertial actuator (10) is introduced into each head (5, 6) so that vibrations due to grinding are damped in said head (5, 6).

4. Active damping centerless grinding method according to any of the preceding claims, characterized in that the active damping force (F _act ) is introduced at the same point of the machine where the vibrations are measured.

5. Active damping centerless grinding method according to the preceding claim, characterized in that vibrations are measured in the upper part of the head (5, 6) and in the upper part of the head (5, 6) The upper part applies the active damping force (F _act ).

6. Active damping centerless grinding method according to any one of the preceding claims, characterized in that the inertial actuator (10) used is a hydraulic actuator, an electromagnetic actuator responsible for accelerating the moving mass or linear motors.

7. Active damping centerless grinding method according to any of the preceding claims, characterized in that vibrations due to grinding are measured using a detection device (9) measuring low frequencies of less than 300 Hz.

8. Active damping centerless grinding method according to the preceding claim, characterized in that the vibrations are measured in the frequency range 10-300 Hz.

9 . Active damping centerless grinding method according to claim 1 , wherein the active damping force (F _act ) is applied along the wheel ( 1 , 2 ) at the component ( 3 ) along the wheel ( 1 , 2 ). 10 . The direction on which the pressure is applied is introduced.

10. Active damping centerless grinding method according to any one of the preceding claims, characterized in that the active damping force (F _act ) introduced is proportional to the speed of the vibration due to grinding that has been measured, And it is introduced at the same frequency and at the opposite phase relative to the velocity of the vibration measured.

11. Active damping centerless grinding method according to any one of claims 1 to 9, characterized in that the introduced active damping force (F _act ) is the frequency (ω _a ) in the virtual passive mass and all the A function of relative damping (ξ _a ) is required so that the behavior of passive dampers is simulated virtually.

12. Active damping centerless grinding method according to the preceding claim, characterized in that the active damping force (F _act ) is a function of the following equation:

in:

m is the mass of the grinder,

μ is the ratio between the virtual passive mass m _a of the inertial actuator and the mass m of the machine (μ=m _a /m),

x is the motion measured due to vibration,

ω _a is the desired oscillation frequency in the virtual passive mass,

ξ _a is the desired relative damping in the virtual passive mass.